The project seeks to further the development of a series of diphtheria toxin mutants which, when employed in the construction of protein fusion toxins, display reduced induction of leakage through vascular endothelial cell monolayers. The goals of this Phase I proposal are to evaluate two, in vivo models of vascular leakage, selecting one model for further in vivo analysis of diphtheria toxin mutants generated by AGI. Successful completion of these studies will result in the determination of modified diphtheria toxin toxophores suitable for protein fusion toxin development and testing in disease-specific, in vivo models. Vascular leakage in humans is a common side effect of fusion toxin therapy and may be inhibiting the development of this class of therapeutic agent. Advances in reduction of vascular leakage could enhance the therapeutic index of these drugs and make them available to a wider population of patients. Currently there is only one FDA approved drug in this class, ONTAK, which is used to treat persistent or recurrent cutaneous T-cell lymphoma. Sales of this drug range between $30 and $40M annually. PUBLIC HEALTH RELEVANCE: This project seeks to develop modified diphtheria toxin interleukin-2 molecules with reduced side effect profiles. In excess of 30% of all patients that currently receive DAB389IL-2, or ONTAK(r), experience vascular leak syndrome. The molecules being developed and tested in these studies will potentially provide a path for the development of the next generation of ONTAK(r) that may be more appropriate for a wider patient population afflicted with a broader range of diseases. [unreadable] [unreadable] [unreadable]